Municipal and agricultural waste disposal is a major problem. For agricultural animals, the animals are confined in high densities and lack functional and sustainable waste treatment systems. The liquid wastes are generally treated in large anaerobic lagoons with intermittent disposal through land applications (Stith, P. and Warrick, J., Boss Hog: North Carolina's pork revolution, The News & Observer, 1-3, February 19-26, 1995; USEPA, Proposed regulations to address water pollution from concentrated animal feeding operations, EPA 833-F-00-016, January 2001, Office of Water, Washington, D.C. 20460). This system was developed in the early and mid 20th century prior to the current trend in high concentrated livestock operations. One of the main problems in sustainability is the imbalance of nitrogen (N) and phosphorus applied to land (USEPA, supra; Cochran et al., Dollars and Sense: An economic analysis of alternative hog waste management technologies, Environmental Defenses, Washington, D.C., 2000). Nutrients in manure are not present in the same portion needed by crops, and when manure is applied based on a crop's nitrogen requirement, excessive phosphorus is applied resulting in phosphorus accumulation in soil, phosphorus runoff, and eutrophication of surface waters (Heathwaite et al., A conceptual approach for integrating phosphorus and nitrogen management at watershed scales, J. Environ. Qual., Volume 29, 158-166, 2000; Sharpley et al., Practical and innovative measures for the control of agricultural phosphorus losses to water: An overview, J. Environ. Qual., Volume 29, 1-9, 2000; Edwards and Daniel, Environmental Impacts of ON-Farm Poultry Waste Disposal—A Review, Bioresource Technology, Volume 41, 9-33, 1992).
The change from small individual animal production operations to large, confined, commercial enterprises has caused many problems for the animal production industry including emission of ammonia (NH3) from lagoons. It may be anticipated that about 50-80% of the nitrogen (N) entering animal lagoons will escape to the atmosphere through NH3 volatilization (Miner and Hazen, Transportation and application of organic wastes to land, In: Soils for Management of Organic Wastes and Waste Waters, 379-425, eds: L. F. Elliot and F. J. Stevenson, Madison. Wis.: ASA/SCCA/SSSA; Barrington and Moreno, Swine Manure Nitrogen Conservation Using Sphagnum Moss, J. Environ. Quality, Volume 24, 603-607, 1995; Braum et al, Nitrogen Losses from a Liquid Dairy Manure Management System, I: Agron. Abstracts, Madison, Wis., ASA, 1997). Biological removal of nitrogen through the process of nitrification and denitrification is regarded as the most efficient and economically feasible method available for removal of nitrogen from wastewaters (Tchobanoglous, G. and F. L. Burton, Wastewater Engineering and Treatment, Disposal and Reuse, Boston, Mass.: Irwin/McGraw-Hill, 1991). The effectiveness of the biological nitrogen removal process depends on the ability of nitrifying organisms to oxidize ammonium ions (NH4+) to nitrite (NO2−) and nitrate (NO3−). Subsequent reduction of molecular nitrogen, denitrification, may be essential as well if one desires to reduce total nitrogen as well as ammonia nitrogen.
Conservation and recovery of nitrogen (N) from wastes is important in agriculture because of the high cost of commercial nitrogen fertilizers. One of the largest environmental concerns with livestock and poultry production is the loss of ammonia gas (NH3) from manure (Aneja et al., 2001; Paerl, 1997). The Research Triangle Institute International (RTI, 2003) estimated the monetized economic benefits to North Carolina households of changes in environmental quality resulting from the generalized adoption of alternative waste technology (2,300 swine operations). Results indicated that adoption of technologies that provide a 50% reduction of NH3 emissions accounts for an estimated benefit of $190 million//year in avoided human health impacts (RTI, 2003).
There is a major interest from producers and the public in implementing best control technologies that will abate NH3 emissions from confined livestock operations by capturing and recovering nitrogen.
Continuing efforts are being made to improve agricultural, animal, and municipal waste treatment methods and apparatus. U.S. Pat. No. 5,472,472 and U.S. Pat. No. 5,078,882 (Northrup) disclose a process for the transformation of animal waste wherein solids are precipitated in a solids reactor, the treated slurry is aerobically and anaerobically treated to form an active biomass. The aqueous slurry containing bio-converted phosphorus is passed into a polishing ecoreactor zone wherein at least a portion of the slurry is converted to a beneficial humus material. In operation the system requires numerous chemical feeds and a series of wetland cells comprising microorganisms, animals, and plants. See also U.S. Pat. Nos. 4,348,285 and 4,432,869 (Groeneweg et al.); U.S. Pat. No. 5,627,069 to Powlen; U.S. Pat. No. 5,135,659 to Wartanessian; an U.S. Pat. No. 5,200,082 to Olsen et al. (relating to pesticide residues); U.S. Pat. No. 5,470,476 to Taboga; and U.S. Pat. No. 5,545,560 to Chang.
Anaerobic digestion (AD) of manures offers many environmental advantages such as biogas production and pathogen destruction. However, the inhibition of methanogens by high ammonia concentration in these wastes severely inhibits the production of biogas (Sung and Liu, Chemosphere, Volume 53, 43-52, 2003; Caller and Winter, Applied Mcirob. And Biotechnol., Volume 48, 405-410, 1997; Koster and Lettinga, Agric. Wastes, Volume 9, 205-215, 1984)
For example, Sung and Liu (2003; supra) observed a substantial drop in methane production at TAN (total ammonia nitrogen) concentration higher than 2000 mg N/L, with drops of 39% and 64% at TAN concentrations of 4920 and 5770 mg/L. The inhibitory boundary of 2000 mg/L TAN was also identified by Koster and Lettinga (1984, supra). The high ammonia nitrogen content of pig manure has been reported as the main reason for low biogas production by Angelidaki and Ahring (Applied Microbiology and Biotechnology, Volume 38, 560-564, 1993), Hansen et al (Water Research, Volume 32, 5-12, 1998), Bonmati and Flotats (Waste Management, Volume 23, 261-272, 2003). Bonmati and Flotats (2003, supra) studied air-stripping pretreatment to reduce ammonia before AD of swine manure. They found that the air-stripping of ammonia before AD significantly reduced the COD by 26-30% and the biogas production potential of the slurry and concluded that air-stripping is not an advisable pre-treatment to pig slurry anaerobic digestion. Even though the inhibition of AD bacteria by high ammonia content in manure wastes is a perpetual problem for the effective implementation of AD in swine, dairy and poultry farms, effective solutions that can remove the ammonia from the liquid effluent without damaging the carbonaceous material used for biogas production have not been found.
The use of bacteria for removal of nitrogen from wastewaters features a combination of nitrification and denitrification processes (Tchobanoglous, G., et al., Wastewater Engineering: Treatment, Disposal, and Reuse. Boston, Mass.: Irwin/McGraw-Hill, 1991). A disadvantage of the nitrification process is that large amounts of oxygen and energy are required to convert all the ammonium (NH4+) to nitrate (NO3−). The subsequent biological reduction of nitrate to nitrogen gas (N2) requires heterotrophic bacteria that utilizes a carbon source to convert NO3− into N2 gas typically under anoxic conditions (Vanotti and Hunt, Transactions of the ASAE, Volume 43(2), 405-413, 2000). Given the high energy costs pertaining to nitrification and the addition of carbon source pertaining to the denitrification process, there is a need to develop a more economical treatment system for effluents containing high ammonium concentrations.
An alternative biological process to N2 production via nitrite (NO2−) reduction is via anaerobic ammonia oxidation. Anaerobic ammonia oxidation is also referred to as anammox. The anammox process was recognized in a wastewater treatment system based on N mass balance (Mulder et al., FEMS Microbiol. Ecol., Volume 16, 177-184, 1995). In the anammox process, under anaerobic and autotrophic conditions, ammonium (NH4+) serves as the electron donor using nitrite (NO2−) as the electron acceptor resulting in production of harmless dinitrogen (N2) gas (Strous et al., Appl. Microbiol. Biotechnol., Volume 50, 589-596, 199; Jetten et al., FEMS Microbiol. Rev., Volume 22, 421-437, 1999). The complete ammonia removal process, or deammonification, entails two sequential reactions: partial nitritation (NH4++1.5 O2+H2O+2H+) and anammox (NH4++1.32 NO2−→1.02N2+0.26 NO3− +2 H2O). Although this anammox equation does not consider other reactants related to cell synthesis (Dongen et al., Water Sci. Technol., Volume 44, 154-160, 2001), it has been used to describe the basic anammox process. Compared to conventional nitrification-denitrification, these combined partial nitritation and anammox reactions save more than 50% of the oxygen supply for nitrification and 100% of the external organic carbon source for denitrification (Furukawa et al., Bioresour. Technol., Volume 100, 5437-5443, 2009). This leads to a significant reduction in energy needs of treatment and a decrease in operational costs. In addition, by-products of anammox do not include greenhouse gases. The partial nitritation can be accomplished with the inhibition of nitrite oxidizing bacteria through limited oxygen supply (Kuai et al., Applied and Environmental Microbiology, Volume 64, 4500-4506), the use of high process temperatures (Dongen et al., The Combined Sharon/Anammox Process, STOWA report, IWA Publishing, London, 2001) or enhancing free-ammonia concentration as a result of high pH and ammonium concentrations (Anthoniesen et al., Journal WPCF, Volume 48(5), 835-852, 1976).
U.S. Pat. No. 6,177,077 (Lee et al.) and U.S. Pat. No. 6,200,469 (Wallace) both relate to the removal of nitrogen and phosphorus from wastewater wherein the phosphate is removed using microorganisms in aerobic tanks which absorb the phosphorus released from denitrified wastewater. See also U.S. Pat. No. 6,113,788 to Molog et al., U.S. Pat. No. 6,117,323 to Haggerty; U.S. Pat. No. 6,139,743 to Park et al.
U.S. Pat. No. 6,893,567 (Vanotti et al.) is directed to a system for treating wastewater to at least reduce the amount of ammonia and phosphorus, as well as at least reducing the presence of infectious microorganisms by using a nirification step to reduce or eliminate carbonate and ammonium buffers contained in the wastewater, precipitating phosphorus using an alkaline earth metal and increasing the pH of the wastewater. See also U.S. Pat. No. 7,674,379 (Vanotti et al.).
Rothrock, Jr. et al. (Transactions of the ASABE, Volume 53(4), 1267-1275, 2010) disclose the removal and recovery of gaseous ammonia from poultry litter using gas-permeable membranes that includes the passage of gaseous ammonia through a microporous hydrophobic gas-permeable membrane.
Szogi et al. developed a treatment process to recover nutrients from animal wastes. The process extracts phosphorus from solid animal wastes such as for example poultry litter or animal manure solids (Szogi et al., published patent application US2009/0193863). The first step of this process extracts phosphorus from solid animal wastes using mineral or organic acids. In the second step, phosphorus is recovered by the addition of liquid lime and an organic poly-electrolyte to the liquid extract to form a calcium-containing phosphorus precipitate.
Gas-permeable membranes have been used in biomedical engineering applications in membrane oxygenator devices to imitate the function of the lungs in cardiopulmonary bypass, to add oxygen to, and to remove carbon dioxide from the blood (Gaylor, 1988). They have also been used to provide waterproof and breathable fabrics in sportswear and footware (GORE-TEX® products, 1968). Brose and Van Eikeren (1990) used gas-permeable membranes in a method for removal of toxic ammonia formed during culturing of mammalian cells. Weiss et al. (1996) used gas-permeable membranes to efficiently aerate surface waters by transferring oxygen without bubble formation.
While various systems have been developed for removing NH3 from wastewater, there still remains a need in the art for different abatement systems that removes NH3 and recovers the N in a concentrated purified form. The present invention, different from prior art systems, provides such systems 20 using hydrophobic gas-permeable membranes and circulated stripping solutions to produce concentrated ammonium salt.